Methods and arrangements in a telecommunications system

Abstract

A method and apparatus in a wireless communication system comprising at least one transmitter provided with at least two antennas and at least one receiving unit provided with at least one antenna and wherein training sequences are transmitted from the at least two antennas of the at least one transmitter to the at least one antenna of the at least one receiving unit. Characterized in that first, prior to the transmission, a training sequence P(k) is Inverse Discrete Fourier Transformed to a sequence p(n). Second, for each antenna branch the Inverse Discrete Fourier Transformed sequence p(n) is cyclically rotated by a predetermined step, said predetermined step being p(n) is cyclically rotated by a predetermined step, said predetermined step being different for each antenna branch to generate cyclically rotated training sequences p(n−n1), p(n−n2). Third, the cyclically rotated training sequences p(n−n1), p(n−n2) are transmitted concurrently from said at least two antennas to the receiving unit. Fourth, at the receiving unit receiving the cyclically rotated training sequences, the received sequences being a superposition of transmitted training sequences, each individually affected by the propagation medium, are used to provide channel impulse response estimates for the transmission from respective antenna.

Description

FIELD OF INVENTION[0001]The present invention relates to communication, and primarily to wireless communication.DESCRIPTION OF RELATED ART[0002]In a radio communication system, a bitstream or a symbol stream is sent on a radio channel from a transmitter to a receiver. Physical limitations of wireless channels, such as bandwith limitations, propagation loss, interference, multipath fading, inter symbol interference and time variance, present a fundamental challenge to reliable communication. Further challenges come from power limitation, size, and speed of devices that are employed within portable wireless apparatus.[0003]It is well known for a man skilled in the art that in most scattering environments, antenna diversity, i.e. the usage of multiple transmitting and / or receiving antennas, is the most practical technique for reducing the effect of multipath fading. The diversity technique involves the provision of a number of replicas of the transmitted signal to the receiver, some re...

AI Technical Summary

Benefits of technology

[0045]An advantage of the invention is that it is bandwith efficient, since merely one synchronization symbol time slot is required for multiple channel transfer estimations.

[0046]An advantage of the invention is that it is latency and processing efficient, since the major parts of the processing of the independent channel estimates, per antenna, are performed concurrently.

[0047]A yet further advantage of the invention is that orthogonality is implicitly ensured for up to N transmit antennas by using the coding by N times (Inverse) Fast Fourier Transforms provided that no channel delay spread exists. This is always true disregarding actual content in the training sequence P(K), which therefore may be optimized for any other purpose, e.g. low peak to average ratio.

[0048]A further advantage of the invention is that hardware complexity is very low, since the major part of the processing relies on hardware functions inherent for a modem used in a OFDM system.

[0049]A yet further advantage of the invention is that the channel estimates are very exact due to the stuffing with zeros where noise is prevalent that acts as a noise attenuation mechanism.

[0050]The term “comprises / comprising” when used in this specification is taken to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

Problems solved by technology

A problem with some existing methods for channel estimation in space time coded systems is that the existing methods consume a lot of bandwith since a training symbol is sent for each transmit antenna.

A further problem with at least one state of the art method using concurrent channel training sequences transmissions is that a preferred estimation technique is very complex both from algorithmic and hardware implementation point of view.

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